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The original Hoberman sphere was built as a kinetic sculpture by Chuck Hoberman. I tried two separate ways of building a Hoberman style sphere out of connectors and axles from the LEGO® Technic sets.
I first tried building a sphere using a four point hinge. Unfortunately, I only had enough pieces to complete one half of a sphere and even then I had to mix #8 axles with #6 axles on the scissor assemblies. The resulting semisphere would expand from a collapsed diameter of about 15" to a full diameter of over 30". This is no where near the efficiency realized in a real Hoberman sphere, but its not bad considering that I am locked in by the geometries of the splined connectors. I have also built a segment of a six point hinge and this one takes even more pieces.
The four point hinge design uses a scissors assembly between each pair of hinges. Each scissor assembly was constructed using four #8 axles, twelve #6 axles, sixteen splined connectors, sixteen piston head connectors, and ten two-sided gray hinge pins. A full sphere requires twelve scissor assemblies. The angles used when fixing the splined connectors was one notch from straight and resulted in a right angle assembly.
The hinges are arranged in pairs consisting of inner and outer hinges. The hinges are constructed like pinwheels out of one 2x2 square brick, four 1x2 bricks with pin holes, eight 1x3 plates, and four two-sided gray hinge pins. The outer hinges are constructed with the spokes on the right side and pins extending left and the inner hinges are constructed in the opposite direction. A full sphere requires six pairs of hinges.
The scissor assemblies are connected to the pins on the inner and outer hinges and the sphere is opened by moving the inner hinges apart and closed by drawing them together. While this requires a lot of parts, it is quite interesting to watch it expand and contract and it is relatively stable.
The six point hinge design requires so many parts that I was only able to make a small section of a sphere and was quite limited on the degree of curvature I could obtain. Each scissor assembly had only one hinge point rather than the four hinge points in the first attempt. The hubs were constructed out of the large pulley with six holes, six black connector pins, six splined connectors, six #2 axles, six piston head connectors, and six two sided hinge pins. Like the four point hinge design, the inner and outer hinges were in opposite directions. With additional parts I would have been able to add additional scissor sections between the hinges and increase the angle from one hub to the next. This would create greater curvature between the sections and increase the appearance of a sphere. This design was much tighter than the four point hinge design and opened and closed much more smoothly.
If you're interested in any additional information on Hoberman spheres, I recommend that you visit their site at http://www.hoberman.com.
